Bottoms of ships, underwater structures, fishing nets, etc. are exposed to water for a long period of time, so that various aquatic organisms, e.g., animals such as oysters, mussels and barnacles, and plants such as seaweeds and bacteria, are liable to adhere to their surfaces and propagate thereon. If such animals and plants adhere and propagate, not only appearances of the ship-bottoms, underwater structures, fishing nets, etc. are deteriorated but also functions thereof are impaired.
Particularly in the case where such aquatic organisms adhere and propagate on the bottom of ship, surface roughness of the whole ship is increased to sometimes induce lowering of ship velocity and increase of fuel consumption. Further, in the case where bacteria, slime (sludge substances) or larger organisms adhere and propagate on the surfaces of underwater structures such as steel structures, the structures may be corroded or the anti-corrosion coating films on the underwater structures may be damaged, that is, there is a fear that the strength, functions and lifetime of the underwater structures are markedly lowered. For removing such aquatic organisms from the underwater structures, much labor and working time are required.
In order to prevent such damages, coating of the base materials of ships, underwater structures, etc. with antifouling paints has been heretofore carried out. The existing antifouling mechanisms of the antifouling paints are broadly divided into a mechanism of extraction type (diffusion type) wherein an antifouling agent is extracted from a coating film and a mechanism of a self-polishing type wherein a surface of a coating film is renewed to bring a fresh antifouling agent into contact with seawater. The extraction type has disadvantages of increase in surface roughness and a short period of antifouling time.
Therefore, the antifouling paints of self-polishing type are preferably employed for the base materials of ships, underwater structures, etc. which require long-term antifouling property. In case of the antifouling paints of self-polishing type, the surface of the resulting coating film is dissolved little by little, so that the coating film surface can be maintained smooth. Moreover, there is an advantage that by controlling the dissolution rate of the coating film, the elution rate of the antifouling agent can be controlled over a long period of time, and thereby excellent antifouling property can be maintained for a long period of time.
As such an antifouling paint of self-polishing type, an antifouling paint composition comprising rosin which is collected from natural pine and a synthetic resin which serves to reinforce strength of a rosin-based coating film is known.
The rosin is a natural compound containing abietic acid and its isomer as main ingredients, and it is known that the rosin is slightly soluble in seawater. Such rosin is widely employed as a resin for an antifouling paint.
For example, in Japanese Patent Laid-Open Publication No. 30071/1998 (patent document 1), a paint composition containing, as essential ingredients, one or more compounds selected from rosin-based compounds such as rosin, rosin derivatives and rosin metal salts, an organic silyl ester group-containing polymer and an antifouling agent is disclosed. In this publication, it is described that a coating film made of the paint composition does not cause formation of a residue layer on the surface of the film even after long-term immersion, is free from defects such as cracking and peeling, exerts marine organism adhesion-preventing performance over a long period of time and is excellent in recoating property and marine organism adhesion-preventing performance in the outfit time.
However, the rosin-based compounds are derived from natural substances, so that there are a fear of unstable supply and a fear of exhaustion of resources in the future. Moreover, there is a problem that the rosin-based compounds have variability in qualities and composition attributable to growing district, type of tree, purification conditions, storage conditions, etc., so that it is difficult to obtain antifouling paint compositions of excellent and uniform qualities.
Under such circumstances as described above, the present inventors have earnestly studied for the purpose of developing a novel antifouling paint composition capable of forming an antifouling coating film having proper solubility and long-term antifouling property.
By the way, in the development of an antifouling paint composition, the following problems should be taken into consideration.
First, there has been much more desired than before an antifouling paint composition capable of forming a coating film which can exert high antifouling performance over a long period of time even in the highly fouling environment, because in recent years environmental pollution is getting worse and contamination of seawater near the land has become terrible, and for example, ships must stay in such a terribly contaminated sea area for a long period of time when they stop at ports for charging cargos or during the outfit time (period of time for building an interior of a ship on the sea after building of outside plating of the ship in the dock).
Further, the antifouling paint is sometimes stored for a long period of time after it is put on the market, and also in such a case, it is required that property change and deterioration of the paint do not occur.
The present inventors have earnestly studied aiming at development of a paint composition satisfying all of the above requirements, and as a result, they have found that a specific cyclic carboxylic acid formed by the addition reaction of a specific unsaturated carboxylic acid with a specific conjugated diene compound and a metal salt thereof are novel compounds and that one or more compounds (A) selected from the novel cyclic carboxylic acid, the metal salt thereof and a metal salt of a derivative of the cyclic carboxylic acid are preferable as a compounding agent for an antifouling paint which functions as a hydrolysis controlling agent for an antifouling coating film or an elution assistant for an antifouling agent. The present inventors have further found that an antifouling paint composition comprising the compound (A) such as the cyclic carboxylic acid and a copolymer (B) for a self-polishing type antifouling paint, particularly a silyl ester copolymer, has excellent long-term storage stability, and a coating film formed by applying and curing the composition has a favorable hydrolysis rate, is excellent in long-term antifouling property in the static environment or the dynamic environment and has an excellent balance of these properties. Based on the finding, the present invention has been accomplished.
Patent document 1: Japanese Patent Laid-Open Publication No. 30071/1998